"The government of South Sudan accepted," Mahboub Maalim said after a summit in the Ethiopian capital, Addis Ababa, adding that the specific scope and mandate of the force had yet to be decided.
But once an agreement on that had been reached, it would be submitted to the UN Security Council for a vote.
The force could be used to help implement an August 2015 peace deal, while protecting civilians and carrying out humanitarian duties, Maalim said.
Fighting from August 8 to 11 left 300 people dead and forced more than 60,000 others to flee their homes.
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Regional bloc IGAD had raised the possibility of deploying an "intervention brigade" with a more aggressive mandate within the UN mission currently present.
The 12,000-strong UN peacekeeping mission in South Sudan, UNMISS, has faced criticism for failing to stem the latest bloodshed or fully protect civilians during the fighting.
Former vice-president Machar has refused to come back to Juba until the deployment of a neutral force of African troops -- a plan approved by the the US and African Union but until now rejected by Kiir.